The present invention relates to printed circuit board manufacturing and in particular to an apparatus and method for depositing various patterns on printed circuit boards using jet-dispensing technology.
There follows a list of references that is referenced in the following description.
1. Sematech Dictionary (http://www.sematech.org/public/publications/dict/con_to_cz.htm)
2. Circuit Board Terminology (http://www.sdcbs.com/term.htm)
3. Institute for Interconnecting and Packaging Electronic Circuits (IPC), Lincolnwood, Ill.
4. SMEMA 7 Fluid Dispensing Terms and Definitions (http://ipc.org/html/smemastandards.htm)
5. SMEMA 3.1 Fiducial Mark Standard (http://ipc.org/html/smemastandards.htm)
6. Printed circuits handbook, /Clyde F. Coombs, Jr., editor-in-chiefxe2x80x943rd ed. ISBN 0-07-012609-7
7. U.S. Pat. No. 5,637,426 Uchikawa June 1997
8. U.S. Pat. No. 4,668,533 Miller May 1987
9. Laid-Open (Kokai) No. Hei 9-18115, Niijima January 1997, Japan
10. U.S. Pat. No. 4,767,489 Lindner August 1988
11. U.S. Pat. No. 5,270,368 Lent et al, December 1993
12. Laid-Open (Kokai) No. Hei 11-87883, Takada et al., March 1999, Japan
13. U.S. Pat. No. 4,748,453 Lin et al., May 1988
14. U.S. Pat. No. 4,963,882 Hickman, October 1990
15. U.S. Pat. No. 4,999,646, Trask, March 1991
16. U.S. Pat. No. 5,239,312, Mema et al., August 1993
17. U.S. Pat. No. 5,790,150 Lidke et al., August 1998
18. U.S. Pat. No. 5,587,730, Karz, December 1996
19. U.S. Pat. No. 5,984,455, Anderson, November 1999
20. U.S. Pat. No. 6,030,072, Silverbrook, February 2000
There follows a glossary of terms used in the following description. The definitions of the terms are given for convenience of explanation and should not be regarded as binding.
The present and ongoing trend of miniaturization and sophistication in electronics and the proliferation of electronic devices in almost all aspects of modern technology have led to stringent demands on the manufacturing of electronic equipment. Mass production of complex systems, incorporating steadily increasing component density in a competitive environment, required automated volume manufacturing procedures of electronic equipment.
The platform that fixates, connects and interfaces most electronic components with each other and with other elements in inter alia, computers, communication devices, consumer electronics, automated manufacturing and inspection equipment, is the printed circuit board (PCB) or printed wiring board (PWB). The manner in which these circuit boards are manufactured and the procedure of inserting and connecting multiple components of large variety (inter alia, resistors, capacitors; and integrated circuits), can be applied in mass production environments, achieving substantial automation, which results in costs reduction, high reliability and high component packaging densities. Backplanes and panels (interconnecting boards, in which printed circuits, panels or integrated circuit packages can be plugged or mounted into or onto) are also manufactured in a similar manner.
Whilst in the beginning of PCB usage, PCB""s embodied substantially few components and moderately simple connecting path structures, modern highly dense populated boards require sophisticated and high resolution manufacturing techniques with precise registration capabilities.
To understand the technology of the present invention, a brief discussion follows of the prior art of a common manufacturing process of PCB""s and in particular, solder masks and legend process.
Briefly, a PCB at the onset of the manufacturing line constitutes a base of insulating material on which a thin copper layer is laminated or plated, known as a bare copper plated board. A chemical etching step removes selectively areas of the copper to produce paths, which are electrically conducting. This selective removal is achieved by covering the copper layer with a patterned mask (etch-resist) that protects the copper layer in the following etching step. Generally, screen-printing techniques are utilized to form the patterned mask in low end PCB""s. In high-end, more densely populated PCB""s having generally complicated multi-layer conducting paths, Liquid Photo Imageable etch and solder resist mask procedures (discussed in more detail below) are commonly utilized. UV curing and subsequently developing produced resist masks with predefined patterns. The pattern that remains on the board after the etching step is commonly known as the primary image conductor pattern.
Whilst etch resist masks protects the areas of the conducting paths during the above-mentioned etching step, the solder resist mask protects the conducting paths from being coated with solder during the soldering step. The soldering step commonly connects the components leads to predetermined positions in the conducting paths (commonly called lands or pads) by fixating the leads and the conducting paths, utilizing a molten metal alloy, which after solidifying, achieves a permanent electrically conductive bond. In mass production commonly wave-soldering methods are utilized. In wave-soldering the PCB passages through a molten solder wave that coats the pads and leads and thus forms the required solder joints. The solder resist mask leaves only the pads uncovered that need to be covered by the molten solder, otherwise, also the conducting paths would be covered with solder, causing several problems such as inter alia, short cuts by bridging solder.
It should be mentioned here that in modern manufacturing methods, such as e.g. SMT and HASL the above-mentioned solder mask retains its protective function.
The solder resist functions in addition also as a protection from the environment (especially from humidity) during the serviceable life of the board as commonly the entire PCB is covered by the solder resist, except for the above-mentioned pads. It should be mentioned that a multitude of additional functions are expected or preferred to be performed by the solder mask; and are described in more detail in the Printed Circuits Handbook, Chapter 16 [6]. The Printed Circuits Handbook also mentions the classification in accordance with ANSI/IPC-SM-840 specification, dividing solder mask performance into three classes:
Class 1: Consumerxe2x80x94Noncritical industrial and consumer control devices and entertainment electronics
Class 2: General industrialxe2x80x94Computers, telecommunication equipment, business machines, instruments; and certain noncritical military applications
Class 3: High reliabilityxe2x80x94Equipment where continued performance is critical; military electronic equipment.
A person versed in the art is thus aware that solder mask properties have significant bearings on the final product properties and performance.
Before component population and subsequently soldering, the PCB legend is printed on the board to support inter alia, identification, repair, verification and field service of unserviceable boards. The PCB legend includes component ID, polarity marks, frames that indicate physical location of components on the board; and sometimes, additional information such as company name, PCB version; and functional instructions such as a jumper function, description of connectors, etc.
Having described briefly the basic steps in manufacturing, there follows now a description of the prior art coating techniques and related problems of resists and in particular, solder resists. It should be mentioned that the difference in usage between etch resist and solder resist is relatively small as both are functionally masks that need to protect selected areas from certain interactions with etchants, solders, chemical reducing agents, or other external influences.
There are permanent and temporary types of solder resists. The temporary solder resists are usually applied to selected areas and consist commonly of a latex rubber material or any of a variety of adhesive tapes. Commonly, temporary solder resists are applied by manual- or automatic-dispensing methods using typically pre-formed xe2x80x9cpatchesxe2x80x9d or strips. By keeping solder out of selected holes, the temporary resists allow temperature or process-sensitive components to be added later. Removal of temporary solder mask is based on the properties of the temporary solder mask. Some of the temporary solder masks are peelable, whilst other are soluble in subsequent cleaning steps, in which cleaning agents are utilized, that also remove such temporary solder masks.
Permanent solder masks are not removed after being applied; and thus become part of the PCB composition and cover substantial areas of the entire PCB. Whilst pre-fabricated dry solder mask films and screen printing techniques are utilized in commonly less demanding low-end products, hi-end are generally manufactured using the Liquid Photo Imageable Solder Mask method (abbreviated commonly to: LPISM) discussed with reference to FIG. 1.
1. After lamination or plating in a previous step of manufacturing line 100, a PCB is transported 101 to the Solder mask station 102.
2. In the cleaning stage 103, surface preparation usually consists of a mechanical brush scrubbing followed by a pumice treatment, solvent degreasing, chemical cleaning and finally, oven drying.
3. Coating the PCB by LPISM material 104 is performed in the coating stage 105. The coating can be applied to the board by inter alia, blank (no pattern) screen printing, roller coating, curtain coating, or electrostatic spraying.
4. Partially curing the coating, to achieve a tack-free (non-sticking) coating is performed in the drying stage 106.
5. UV Exposure through a photo-tool 107, which was prepared before, and described in more detail below, is performed in the exposure stage 108.
6. Development of the exposed and thus partially hardened mask dissolves and removes the unexposed areas or the exposed areas not hardened by the previous exposure in the developing stage 109.
7. If another method of solder masking is utilized, then some or all steps and stages within boundary 110 are replaced or modified.
8. Final curing stage 111 hardens the mask to perform all functions mentioned above and the PCB is transported 112 to the following station on the manufacturing line 100.
The LPISM process is both capital and labor intensive as can be seen from the list of required equipment:
a. Coating unit (with reference to stage 105)
b. Pre-exposure curing unit (with reference to stage 106)
c. Exposure machine (with reference to stage 108)
d. Developing machine (with reference to stage 109)
e. Conveyors and automated handling equipment for transporting the PCB from each piece of equipment to the next one (113)
To above listed equipment should also be added necessary equipment for photo tool 107, obligatory to produce the optical mask used in above-mentioned exposure stage 108. Opaque and transparent areas are formed utilizing photographic processes and materials, schematically shown in photo tooling station 114.
f. Light sensitive film material 115 is exposed in plotter 116 that images the output from a CAD (Computer Aided Design) workstation or other source onto film material 115.
g. Using appropriate GA (Graphic Arts) processing chemicals film material 115 is processed (inter alia, developed, fixated and dried) in processing stage 118.
As readily arises from the foregoing discussion, there are a multitude of machines, materials and procedures required to complete the solder mask manufacturing stage.
As mentioned above, before the various components are affixed to the PCB, as a last stage in the board manufacturing line is the legend printing station.
Reference is now made to FIG. 3, showing schematically a prior art legend printing process. The required photo tool manufacturing process for screen printing is substantially identical to the photo tool manufacturing process described above in reference to photo tooling station 114 in FIG. 1, and therefore photo tooling station 300 is not further described.
At screen-print tooling station 301 a printing tool is produced that uses the known per se technique of (silk) screen-printing. Screen-printing is widely used because it enables the usage of a wide variety of printing inks and therefore inter alia, is also capable of printing onto a wide variety of substrates. For this reason, screen-printing techniques are preferably used for legend printing. A finely structured net, commonly also called web or mesh, is impregnated or coated with a photo-imageable masking substance 302, commonly called photo resist emulsion, in a coating stage 303. It should be mentioned that screen-printing techniques are sometimes also utilized as a coating technique, because, as mentioned before, a wide variety of inks or in this case, coating substances can be utilized. Therefore, in a screen-print coating process, a xe2x80x9cblankxe2x80x9d type of mask 304 is used, that substantially defines the total area of the surface to be coated. A short drying step 305 ensures that the photo resist emulsion is tack-free (non-sticking). The photo tool mask, prepared in above-mentioned photo tooling station 300 is brought in close contact with the web, being impregnated with the now substantially dry photo resist emulsion and exposed in a commonly used contact UV exposure device 306. The developing stage 307 will effectively remove areas of the photo resist emulsion, not hardened by exposure to UV light. Thus, the web""s numerous holes are now closed or clogged by the photo mask not dissolved in the developing process. The hence prepared web is placed and stretched in a frame of suitable dimensions, before being cured (hardened) in curing stage 308 in order to achieve physical resistance against inter alia, abrasion during the following printing process. Alternatively, the web can be stretched on the above-mentioned frame prior to impregnation with photo resist emulsion and consequent exposure. Significant physical resistance is desired and required as will become evident from the brief discussion of the following screen printing step. Curing is commonly achieved by exposure to elevated temperatures during a determined period of time in a oven. Optionally, curing can be achieved by UV exposure as well, but is rarely utilized due to performance limitations of UV-curable legend inks.
In the screen printing step 309, the above described frame, also known as screen stencil, holding the stretched mesh or web under tension, is brought in close contact with the PCB in preferable precise manner of registration. Suitable legend ink 310 is poured into the frame and a flexible wiper, called the xe2x80x9cdoctor""s bladexe2x80x9d, is moved from one side of the frame to the other. The xe2x80x9cdoctor""s bladexe2x80x9d squeezes effectively the ink through the holes or mazes of the web that were not filled up with hardened photo resist emulsion; and thus, ink is transferred to the surface of the PCB through these holes in a determined pattern. A heating process in oven 311 cures the legend ink and makes it durable and resistant against environmental influences.
Finally, the PCB is transported 312 to a following station in the manufacturing line 313.
Registration problems, related to:
a. positioning the frame and thus the patterned ink transfer onto the PCB;
b. accumulated dimensional distortions of photo tools and stencil screens; and
c. accumulated dimensional distortions of the PCB (xe2x80x9cpotato-chippingxe2x80x9d) induced by modern manufacturing steps, such as laminating, heat treatments, cleaning, etc.
have significantly restricted desired registration precision to unsatisfying levels, whilst the ongoing trend towards higher density circuit boards, requiring more urgently corresponding higher registration precision levels. Especially for Multi Layer Boards (MLB) and Double Sided Boards (DSB), registration is significantly critical as sequentially, multiple imaging steps, inter alia, screen printing and lithographic processes, need to be executed, whilst maintaining desired registration.
Whilst prototyping, above-mentioned hitherto method of manufacturing is especially cumbersome and time consuming, as many alterations are induced to the circuits, necessitating preparation of new photo tools for each and every-alteration. As all above-mentioned manufacturing steps are required for each alteration, manufacturing even a small amount of PCB""s and inducing a few alterations during the prototyping phase, necessitate substantial investments in labor, material and time.
To shorten circuit board production time, a multitude of publications has addressed problems related to photo tooling and/or screen printing usage. U.S. Pat. No. 5,637,426 Uchikawa June 1997 [7] proposes to use an ink jetter to form a mask pattern directly on a transparent mask substrate, thus circumventing the photo tooling steps, but requiring still the above-mentioned cumbersome LPISM process.
There follows now a discussion on known per se ink jet or generally, jetting technologies and some of their specific shortcomings.
The method of jet dispensing of liquid or viscous substances is well known and has been applied in many fields of technology and today, low-cost, high quality text, graphics and photo-image printing equipment is widely in use, particularly in home and office. Many improvements have made this method significantly adaptable for a wide range of applications and liquid or viscous substances. One out of many publications related to the PCB manufacturing is U.S. Pat. No. 4,668,533 Miller May 1987 [8], disclosing image corollary deposition of ink onto a substrate such as a circuit board, by ink jet technology in a two-step process in which the ink is employed either as an activator or as a sensitizer.
In Japanese Laid-Open (Kokai) No. Hei 9-18115 January 1997, Niijima [9] discloses a resist pattern (for etch resist or solder resist) forming method directly on a board using an ink jet printer, thus circumventing the photo tooling as well.
For single prototype or experimental boards U.S. Pat. No. 4,767,489 Lindner August 1988 [10] discloses a small, compact computer-aided printer-etcher that inter alia, applies a resist pattern of meltable wax or thermoplastic material in a jet dispensing manner.
Suitable UV-curable ink compositions for etch-resists are disclosed in U.S. Pat. No. 5,270,368 Lent et al, December 1993 [11].
In Japanese Laid-Open (Kokai) No. Hei 11-87883 March 1999, Takada et al. [12] disclose an ink jet printing method for solder resist and legend patterns in small lot and trial-stage (prototyping) applications, using UV-curable inks.
Another aspect of ink jet printing is the issue of ink area coverage. Many publications have addressed this issue and in particular for forming images on overhead projection transparency film type of media. Lin et al. [13] mentioned that for projection purposes intense color saturation is desirable and achievable by total ink area coverage and overlapping of spots (the ink dots produced on the media by the ink jet printer). Lin et al. teach that this high quality printing is achievable by avoiding xe2x80x9cwhitexe2x80x9d spaces between spots. This is accomplished by two passes of the print head per printing line and selecting a spot size diameter that is substantially equal to 2 times the pixel center-to-center distance. Thus, diagonally adjacent spots will just touch while horizontally and vertically adjacent spots will overlap, resulting in 100% pixel area coverage.
In U.S. Pat. No. 4,963,882 Hickman [14] discloses methods to alleviate known per se problems of print quality degradation with extended use of ink jet print heads. Different strategies are disclosed to improve print quality and methods are described that are resistant to degradation of print quality with extended use of print heads. Essentially, a double dotting approach (deposition of two dots of a single color in a single pixel row are formed using droplets from different nozzles, so that the degradation in image quality due to a failed nozzle is significantly reduced. The advantages are obtained at a reduced quality level, meaning the print resolution is being reduced.
Trask in U.S. Pat. No. 4,999,646 [15] discloses improvements in print quality and color uniformity as a direct result of improvements in uniformity and consistency of dot formation. Trask recognizes that inter alia, nozzle direction errors, ink drop volume variations, paper motion errors, and carriage motion errors induce problems related to print quality, ink area coverage and other problems related to imaging on paper and other media. To alleviate these problems Trask proposes to use a combination of:
a. super pixeling in the overlying printed areas to generate dot-next-to-dot (DND) printed images, and
b. providing complementary and overlying swath (printed strip or line) patterns of ink jet print.
Merna et al. in U.S. Pat. No. 5,239,312 [16] address the undesirable xe2x80x9cbandingxe2x80x9d and xe2x80x9cseamingxe2x80x9d by introducing a unique row-interleaved printing method and system, minimizing the non-uniformity in solid patterns.
Lidke et al. [17] disclose a method for selectively printing only a portion of the print dots in a multi-pass printing mode. The method relates to providing pixel data to the print head in accordance with a predetermined firing sequence for a plurality of print nozzles that comprise the print head for each of a plurality of print cycles.
Karz [18] discloses a thermal ink jet printer having redundant printing capabilities by virtue of utilizing a secondary print head. In one mode both print heads supplement each other, whilst in another mode, the second print head backs up the first print head in event of malfunction.
The ongoing demand for greater printing speeds has induced further predicaments such as critical nozzle alignment and nozzle malfunctioning due to increased amount of nozzles and increased nozzle column length of print heads. To minimize these problems, Anderson in U.S. Pat. No. 5,94,455 [19] proposes to utilize an ink jet printing apparatus having primary and secondary nozzles. The secondary nozzles define redundant nozzles addressing nozzle malfunctions and enable furthermore increased printing speed in a non-redundant nozzle printing mode. In the redundant (normal) print speed mode, the printing task of a malfunctioning nozzle is taken over by its associated nozzle on the same horizontal line. Furthermore, Anderson also contemplates to provide a nozzle testing station that tests each individual nozzle on functionality.
Recently, the demand for digital printing presses have lead to many publications related to improvements in ink jet technology, to suffice the stringent demands for high volume and simultaneously, high quality ink jet printers. Silverbrook [20] discloses methods of reducing xe2x80x9cdowntimexe2x80x9d of printing lines by virtue of including at least one spare printing module. Silverbrook also mentions that pagewidth static print heads containing thousands of nozzles benefit significantly from fault tolerance by virtue of redundant nozzles. In consonance with Hickman and Anderson, Silverbrook also mentions the increase of printing speed by using a multitude of nozzles. Moreover, Silverbrook teaches that for high quality printing at lower resolution the amount of ink deposited is directly proportional to the number of dots printed.
It should be noted that all publications mentioned above related to PCB manufacturing, either focus on UV-curable ink compositions or disclose substantially only the method of ink jet printing, in foremost, single or small lot prototyping or experimental circuit board manufacturing applications. However, mass production PCB manufacturing procedures have not yet been disclosed, capable of utilizing advantages of jet dispensing resist mask or legend printing technology for fast, reliable and high quality volume manufacturing, because prerequisites have not yet been met by prior art techniques. Such prerequisites are inter alia, high resolution with zero fault tolerance, position repeatability with very low tolerances, and jettable substances suitable for resist masks.
There is accordingly a need in the art to provide for a jet dispensing system and method that substantially reduces or eliminates the limitations in hitherto known solutions and provides solutions in industrial scale PCB""s manufacturing lines of dispensing a determined pattern of various substances and which is also applicable to large sized boards and back planes as well.
It should be noted that applicable ink jetting methods for industrial PCB manufacturing should preferably, although not necessarily, address the issues of:
1. print quality
(a) resolution:
(i) at least 300xc3x97300 dpi for legend imaging;
(ii) at least 600xc3x97600 dpi for various etch and solder masks;
(b) ink area coverage, especially but not limited to etch and solder masks:
(i) substantially reducing the possibility of pinholes and/or uncovered areas;
(ii) sufficient ink deposit to utilize the deposited image for masking purposes;
(iii) optimizing uniformity (absence of xe2x80x9cbandingxe2x80x9d and/or xe2x80x9cseamingxe2x80x9d) of solid areas (foremost masks);
(c) distortions:
(i) reducing ink droplet distortions due to their relative x-velocity component of travel, upon contact with the print surface;
(ii) compensating for dimensional distortions of PCB (xe2x80x9cpotato-chippingxe2x80x9d) due to foregoing manufacturing steps of the PCB;
2. throughput:
(a) outfitting the PCB printer with significantly enough nozzles to:
(i) achieve required resolution at an inherent redundancy to avoid multiple print passes;
(ii) accomplish desired print area coverage with desired amount of ink at, preferably a minimal number of print passes (swaths);
(b) aligning print pattern with a PCB xe2x80x9con-the-flyxe2x80x9d, thus minimizing handling and positioning of PCB prior to printing;
3. specific PCB manufacturing requirements:
(a) compensating for PCB dimensional distortions or xe2x80x9cpotato-chippingxe2x80x9d, enabling accurate registration of printed patterns;
(b) maintaining the PCB flatness within predefined tolerances during printing by sufficient vacuum suction force, enabling sustaining optimum working distance between PCB and print head;
(c) enabling printing of large size PCB""s (e.g. up to 24xc3x9730xe2x80x3) in preferably, one substantially continuous printing step;
(d) enabling a variety of imaging onto PCB""s such as inter alia:
(i) etch resist masks,
(ii) solder resist masks,
(iii) plating resist masks,
(iv) legend print,
(v) peelable, temporary masks,
(vi) conformal coatings,
(vii) solder paste printing,
(viii) laminates and conductors,
(ix) PCB holes and via-plugging;
(x) direct printing of resistors and/or capacitors components,
(xi) edging non-uniformity compensation control,
(xii) underfill,
(xiii) bare die and chip-on-board encapsulation,
(xiv) CSP encapsulation, and
(xv) adhesive depositing.
The present invention in various embodiments, provides for an industrial ink jet system and for methods, to print the legend (marking and/or nomenclature) and the solder resist (solder mask) on Printed Circuit Boards (PCB""s), including backplanes and panels, utilizing jettable ink compositions. Suitable ink compositions are inter alia: melamine, epoxy, and acrylate inks, each curable either by UV exposure, by heat treatment or/and by a combination of several curing mechanisms. It is noted here, that the present invention is not bound to the use of above-mentioned ink compositions and/or any particular curing procedure.
By one embodiment, the system utilizes a horizontally static and rigid printing bridge, containing multiple industrial print heads, constituting a substantial number (preferably several thousands) of ink jet nozzles. By utilizing a horizontally static and rigid printing bridge, reliability problems induced by acceleration and de-acceleration of moving printing bridges is significantly avoided. The system in addition, utilizes an abundant amount of nozzles for providing a multiple redundancy that is able to address the known per se problem of nozzle malfunctions such as clogging and misfiring. The firing delay between even and uneven numbered nozzles is modified from the manufacturer""s recommended values for a determined relative velocity between print head and target surface. Thus, for example, for a determined nozzle gap value and a determined relative print head target surface velocity, a firing delay of 50 xcexcsec is indicated for achieving a known per se desired dot pattern coverage. By decreasing the firing delay a dot pattern is achieved that is characterized by substantially overlapping of adjacent dots, inducing an inherent redundancy and furthermore, provides the desired ink amount for satisfying masking quality. As this would lower the achievable print resolution by the factor of redundancy, it is noted that the system is equipped with a printing resolution capability higher by the same factor of redundancy, achieving effectively the preferred print resolution, whilst maintaining fault tolerance.
The system in a preferred embodiment is capable of accepting and printing onto any size of PCB up to and including backplane and panel sized (e.g. 24xc3x9730 inch) boards, utilizing a vacuum table movable in both x- and y-directions at high velocity and high precision. Furthermore, In order to keep the nozzle orifice of the print heads at optimum working distance from the print target, the horizontally static and rigid printing bridge is capable of moving vertically in the z-direction (perpendicular to the target surface) to accommodate for PCB""s having various thickness dimensions. Prior to starting a print job, the rigid printing bridge is set to a predetermined position to accommodate various panel/board thickness, as the optimum jetting distance should be retained between 0.8 and 1 mm.
Furthermore, the vacuum table of the present invention, in accordance with a preferred embodiment, is equipped with a multitude of vacuum inlets, each inlet coupled to a suction zone. Thus, area-addressable suction force is achieved for:
1. achieve necessary PCB flatness within predefined desirable tolerances, if, due to mechanical and heat treatments during the consecutive manufacturing steps, a PCB lacks the necessary flatness. Thus, for PCB""s not covering the total vacuum table area, sufficient suction force can be applied to solely the area the PCB covers.
2. temporarily switching in correspondence with the area wherein currently ink is being deposited to a predefined reduced suction force system. Thus, the known per se problem of suction by numerous holes existent in PCB""s on which solder masks or/and legend print is being deposited is substantially alleviated.
The system of the present invention, in accordance with preferred embodiments, is equipped with a vision system comprising of a vision processor unit and a vision registration and distortion compensation unit, addressing the common problems of:
a) achieving PCB alignment with the printed pattern and
b) compensating for PCB dimensional distortions.
By adjusting (rotating) the print image, global registration at a desired precision is achieved without necessitating the PCB to be positioned in a precise defined manner. The software of the present invention, in accordance with the preferred embodiment, is furthermore configured with skewing algorithms to achieve full alignment with inter alia, fiducial marks, according to substantially all IPC (Institute for Interconnecting and Packaging Electronic Circuits) standards. Furthermore, the vision system provides high precision global alignment of both legend and solder resist patterns to the PCB dimensional features, enabling the printing step to commence without placing the PCB in a significantly precise predefined position.
In addition, the vision system provides for autonomous identification of malfunctioning nozzles by utilizing a suitable test print pattern that has been printed by preferably, all nozzles. Thus, respective malfunctioning nozzles are identified and consequently, shot down by the system. The system calculates the remaining redundancy and if a predefined redundancy level is not achieved, an appropriate alert signal is generated.
By providing in one embodiment of the present invention, twice as many nozzles as required for a certain print resolution, clogged nozzles, consequently shut down, will not affect print quality (in this context, substantially no degradation in edge straightness, a common result from lower print resolution). The print quality is not affected by virtue of covering each targeted area by at least two dots, coming from two nozzles, achieving that every nozzle is backed up by at least one other nozzle. In one embodiment of the present invention a modified firing timing is utilized and thus uneven row orifices of the same jet print head function as xe2x80x9cbackupxe2x80x9d for the even row orifices or vice versa. In another embodiment, each jet print head of a row of jet print heads is backed up by another jet print head, positioned opposite in a parallel row of jet print heads. In yet another embodiment, a color ink jet print head is utilized, capable of jetting multiple colors simultaneously. By utilizing the same ink for each color conduit, multiple redundancy as described above is correspondingly achieved.
Jettable compositions such as inter alia, melamine, epoxy, and acrylate inks, each curable either by UV exposure, by heat treatment, or/and by a combination of several curing mechanisms, are preferably utilized in the system of the present invention.
The system according to one embodiment of the present invention constitutes a printer console and an operator console, coupled to the printer console by means of cabling.
Notwithstanding improvement in printing speed, it has not as yet reached a desired level, and accordingly, the printing speed still constitutes bottlenecks in high volume manufacturing lines. Thus, in accordance with another embodiment of the present invention, one central operator console commands a multitude of printer consoles, averting bottlenecks by distributing in a parallel manner the printing step to more than one printer.
In another embodiment, the system of the present invention is a stand-alone system and thus the printer console contains substantially all systems.
Those versed in the art will readily appreciate that the present invention enables significantly simpler and less cumbersome resist masks and legend printing procedures than common prior art procedures, described above and in reference with FIGS. 1 and 3 as will become apparent by the description below.
Accordingly, by one aspect of the present invention there is provided: a jet dispensing print system for dispensing a liquid or viscous, jettable substance as a pattern onto the surface of a platform in an industrial manufacturing production line, comprising:
(A) a printing system, that includes:
(I) a printing bridge system, comprising a static and rigid printing bridge to accommodate in a precise manner several jet print heads, each being fitted with a multitude of jet nozzles, said jet print heads grouped in various arrangements on said static and rigid printing bridge, said jet print heads are utilized achieving multiple redundancy whereby part of the total amount of available nozzles are utilized as back-up nozzles; and
(II) a platform system, comprising:
(a) a printing table positioned substantially underneath said static and rigid printing bridge, for accommodating said platform whilst said pattern is dispensed in a jetting manner onto said platform; and
(b) a motorized system, for moving said printing table simultaneously in at least two perpendicular directions; and
(B) a supply system for supplying said several jet print heads with said liquid or viscous substance; and
(C) a control system responsive to at least pattern and platform data for controlling said platform system in order to achieve said dispensing of said liquid or viscous, jettable substance as said pattern onto said surface of said platform; and
(D) a user interface for at least providing a status report of said printing system.
Accordingly, by another aspect of the present invention there is provided:
A jet dispensing print method for dispensing a liquid or viscous, jettable substance as a pattern onto the surface of a platform in an industrial manufacturing production line, comprising the steps of utilizing:
(A) a printing system, that includes:
(I) a printing bridge system, comprising a static and rigid printing bridge to accommodate in a precise manner several jet print heads, each being fitted with a multitude of jet nozzles, said jet print heads grouped in various arrangements on said static and rigid printing bridge, said jet print heads are utilized achieving multiple redundancy whereby part of the total amount of available nozzles are utilized as back-up nozzles; and
(II) a platform system, comprising:
(a) a printing table positioned substantially underneath said static and rigid printing bridge, for accommodating said platform whilst said pattern is dispensed in a jetting manner onto said platform;
(b) an area-addressable suction force vacuum table;
(c) a motorized system, for moving said printing table simultaneously in at least two perpendicular directions; and
(B) a supply system for supplying said several jet print heads with said liquid or viscous substance; and
(C) a control system responsive to at least pattern and platform data and controlling said platform system for achieving said dispensing of said liquid or viscous, jettable substance as said pattern onto said surface of said platform; and
(D) a user interface for at least providing a status report of said printing system.